No folder is "safe". There are simple apps that let users extract the contents of their device backups made with iTunes. This means that it's trivial to see any file stored by any app on their device.

And there are countless ways to browse an iOS device's files if the iOS device is jailbroken.

So really there is no "safe" folder you can choose to really hide content from a user if the user has the slightest technical ability.

Same for any files bundled in an app. A user can unzip the ipa of any app they've ever installed on any of their iOS devices. All of the ipas are stored on their computer when they backup their device via iTunes.